A New Way to Launch Rockets

[Kurt Eherenman]

Just saw this one. I think I will start launching my rockets with an atlatl, then work my way up to a centrifuge:

https://futurism.com/startup-tests-rocket-launched-by-super-powerful-slingshot/amp

 

[KenECoyote]

Try a pitching or tennis machine first!

 

[viney266]

Well, the Canadian space cannon had potential, if you can keep the release stable...Why not

 

[Grant_Edwards]

Just saw this one. I think I will start launching my rockets with an atlatl, [...]

Throwing a spear with an atlatl is really tricky and requires a lot of practice. I'm pretty sure I could never build enough rockets...

 

[cerving]

This has been covered before, but their whole idea doesn't make sense in so many ways. The write up says

Space startup SpinLaunch has a wild idea: instead of launching rockets vertically from the ground, why don’t we spin them inside a massive centrifuge and use that built up energy to slingshot them to high altitudes, where they can kick on relatively small rocket engines to cover the final distance into orbit? (my bold/italics added)

The thing is that it's VELOCITY, not DISTANCE that gets you into orbit, and throwing something really fast in dense air is basically going to scrub off most of velocity that you started with. That energy is going to go to heat... a lot of it. Now if they put this thing on a balloon and lifted it up to 100,000'...

 

[FredA]

It can be useful to throw a rocket in the air and air-start the motor.
Let the "launch pad" create the initial liftoff velocity - that much less energy that needs to be contained in the rocket.

Takes a smaller motor if you start higher up with non-zero velocity and lower air density.
Think of this as a two-stage rocket with an unconventional booster.

Good idea if the "hardening" of the rocket to survive the weird forces doesn't add too much penalty or payload restrictions.

 

[Grant_Edwards]

This has been covered before, but their whole idea doesn't make sense in so many ways. The write up says

[...]relatively small rocket engines to cover the final distance into orbit? (my bold/italics added)

The thing is that it's VELOCITY, not DISTANCE that gets you into orbit,

Yea, that's what I yelled (silently) at the screen when I read that. At that point I pretty much assumed the entire article was sans clue.

and throwing something really fast in dense air is basically going to scrub off most of velocity that you started with.

Exactly! The "slinghshot" approach has the absolute worst-case velocity vs time/altitude profile. You want to start out slowly in dense air and speed up as you get higher into less dense air.

That energy is going to go to heat... a lot of it. Now if they put this thing on a balloon and lifted it up to 100,000'...

... at the equator [for a free 1000mph bonus].

 

[Kurt Eherenman]

This has been covered before, but their whole idea doesn't make sense in so many ways. The write up says

Space startup SpinLaunch has a wild idea: instead of launching rockets vertically from the ground, why don’t we spin them inside a massive centrifuge and use that built up energy to slingshot them to high altitudes, where they can kick on relatively small rocket engines to cover the final distance into orbit? (my bold/italics added)

The thing is that it's VELOCITY, not DISTANCE that gets you into orbit, and throwing something really fast in dense air is basically going to scrub off most of velocity that you started with. That energy is going to go to heat... a lot of it. Now if they put this thing on a balloon and lifted it up to 100,000'...

Yup. All things seem silly at the onset. I'll include electric cars in a very long list of things that just take time, energy, talent, expertise, experience and a whole lot of money to figure out. Though I don't hold my breath, I am always amazed when things finally work out... like billionaires launching their asses into space.

 

[Grant_Edwards]

Yup. All things seem silly at the onset. [...]

Yea, but writing about "distance into orbit" is going to be silly forever, because the laws of physics are like that. And people who write things like that don't deserve to be taken seriously.

 

[Kurt Eherenman]

Yea, but writing about "distance into orbit" is going to be silly forever, because the laws of physics are like that. And people who write things like that don't deserve to be taken seriously.

Rules were meant to be broken.

 

[Grant_Edwards]

Rules were meant to be broken.

When it comes to Newton's "rules" of physics, trying to break them just doesn't work.

 

[OverTheTop]

Couple of other threads already, with more info and disussion:
https://www.rocketryforum.com/threads/sling-em-into-space.169325/https://www.rocketryforum.com/threads/spinlaunch-receives-prototype-contract-from-dod.153566/

 

[Kurt Eherenman]

When it comes to Newton's "rules" of physics, trying to break them just doesn't work.

The US Navy is working on these "rules" as we speak:

My guess is they can kick these shells straight up... pretty far.

 

[Grant_Edwards]

The US Navy is working on these "rules" as we speak:
[...]
My guess is they can kick these shells straight up... pretty far.

Straight up doesn't get you into orbit.

Orbit isn't "up" orbit is towards the horizon.

The rail gun project had a range of 100 miles compared with existing guns with a range of 30 miles. That's impressive, but it's nothing compared to what it takes to get into orbit.

FWIW, the USN pulled the plug on railgun development:

https://www.defensenews.com/naval/2...-futuristic-railgun-eyes-hypersonic-missiles/

 

[Sandy H.]

[snip]
Now if they put this thing on a balloon and lifted it up to 100,000'...

This is a totally dumb question for sure and is at best a lame 'thought experiment' and at worst the kind of constraints first year engineering students have to solve (i.e. [random problem] assuming that there is no friction, no temperature change, nothing at all affects this simple calculation, even though the real world is not that. . . ).

Assuming money is no object (ha!!!) and that there is land available (somewhat ha), could you build a 20 mile tall 'pyramid' that would let you raise a conventional rocket up that high (or use the salad spinner that is the subject of this thread, no disrespect intended) such that it made access to space more realistic compared to what we're doing now? Ignore constraints related to materials that can't support the weight, ignore the temperature/air density up that high etc. etc. etc.

Basically, what would happen to the rocket equation if we somehow got to start up at 100k feet vs. current ground level. I think percentages would be interesting here (i.e. if Falcon 9 launched from ground it does 100%, if launched from 100k it does 400% or something similar).

Cellphones were impossible 120 years ago. The concept of TikToc would have gotten you burned at the stake back then (as it should today, probably. . .). I'm sure a 40 mile x 40 mile x 20 mile tall pyramid is also impossible today and maybe forever, but if it could exist, what improvement would happen?

Told you it was a dumb question. . .

Sandy.

 

[OverTheTop]

I'm sure a 40 mile x 40 mile x 20 mile tall pyramid is also impossible today and maybe forever

unless we get aliens to help build them like they did in Egypt, only better.

 

[Grant_Edwards]

This is a totally dumb question for sure

Basically, what would happen to the rocket equation if we somehow got to start up at 100k feet vs. current ground level.

That's not a dumb question at all. People who think about stuff like that for a living have asked it. And here's a 2003 paper that shows the SSTO payload weight advantages for launch elevations from 5km to 25km (82k ft):

https://ntrs.nasa.gov/api/citations/20150012328/downloads/20150012328.pdf

The results of the trajectory simulation show that the required propellant loading for a candidate SSTO vehicle decreases as launch altitude is increased, The propellant launch fraction is 87.5% of the gross lift-off mass for a sea-level launch, and decreases to slightly over 85% of the gross lift-off mass for a launch altitude of 25 km above sea level. Since for the candidate SSTO the payload is typically on the order of 2% of the gross lift-off mass, this decrease in required fuel mass can result in over a factor of two increase of payload mass. Even a five kilometer launch altitude, equivalent to launching from the top of a moderate terrestrial mountain, would result in a significant improvement in payload.

Extrapolating from the published data, increasing launch height from 25km to 30km (100k ft) would decrease propellant weight by another 0.5% or so.

Therefore, your answer for the proposed SSTO: If payload weight for sea-level launch is 2%, payload weight for 100k ft launch could be 4.5%.

That's a pretty significant effect.

AFAICT, the benefit is entirely reduced drag loss due to lower air density.

 

[rocket_troy]

The math that historically kills these ideas is the fact that propellant costs are the least significant cost of launching to orbit via historical dinospace lifting.
Of course, as lifting options become more reusable and flight rates start increasing substantially (maybe), then propellant will become a larger slice of the cost pie and the math changes.

TP

 

[Grant_Edwards]

The math that historically kills these ideas is the fact that propellant costs are the least significant cost of launching to orbit via historical dinospace lifting.

You're right: nobody cares about the option to reduce propellant by 2% — that's nothing compared to the cost of a launch.

But, if you can double your payload weight, then you've cut your per-kg launch cost in half.

You can orbit 2 satellites instead of 1.

That's what's significant.

 

[Pete.D]

I imagine that the additional physical forces on the airframe would be very substantial. The rocket would have to be accelerated to a large fraction of orbital velocity, so both centrifugal and drag forces would be enormous. Thermal issues resulting from the atmospheric drag would also be a major factor. The weight of structural improvements and shielding would surely cancel out any gains in payload. Such a system could be practical for a robust payload.

Even if a gun-type launcher were used the structural strengthening required would be substantial.

A better idea could be to use a really high-power laser on the ground to deliver a much more continuous modest acceleration up to nearly orbital speed. You might need more than one, if the acceleration had to continue beyond line-of-sight from the launch pad. The rocket would still have to carry simple reaction mass, but significant savings would result from keeping the energy source on the ground. Kind of like a nuclear rocket without the fallout radiation, but radiation shielding would still be required. The laser is likely beyond the current state-of-art, but I don't see any other roadblocks.

 

[Alan15578]

Exactly! The "slinghshot" approach has the absolute worst-case velocity vs time/altitude profile. You want to start out slowly in dense air and speed up as you get higher into less dense air.

I dissagree, but then I don't know what their launch velocity is or other details. Certainly you do want to speed up as you get into less dense air, but I see the real problems as launch loads and heavy vehicle structural requirements, and the high infrastructure investment for low launch rates.

 

[neil_w]

Scott Manley did a video recently about this system:

The video addresses many of the obvious concerns about how to make this work. Overall, he was far less negative towards it than I expected. I'm still very skeptical.

 

[dhbarr]

That's not a dumb question at all. People who think about stuff like that for a living have asked it. And here's a 2003 paper that shows the SSTO payload weight advantages for launch elevations from 5km to 25km (82k ft):

https://ntrs.nasa.gov/api/citations/20150012328/downloads/20150012328.pdf



Extrapolating from the published data, increasing launch height from 25km to 30km (100k ft) would decrease propellant weight by another 0.5% or so.

Therefore, your answer for the proposed SSTO: If payload weight for sea-level launch is 2%, payload weight for 100k ft launch could be 4.5%.

That's a pretty significant effect.

AFAICT, the benefit is entirely reduced drag loss due to lower air density.

Buying a mountain in the Andes and installing a hyperloop is probably cheaper than Ye Pyramide. Still not as cheap as methalox though unless the launch volume goes WAAAAAY up.

 

[OC-Patrick]

neat idea, but what payloads can even survive the centrifugal forces before it is released? certainly not humans.

 

[cerving]

That's not a dumb question at all. People who think about stuff like that for a living have asked it. And here's a 2003 paper that shows the SSTO payload weight advantages for launch elevations from 5km to 25km (82k ft):

https://ntrs.nasa.gov/api/citations/20150012328/downloads/20150012328.pdf



Extrapolating from the published data, increasing launch height from 25km to 30km (100k ft) would decrease propellant weight by another 0.5% or so.

Therefore, your answer for the proposed SSTO: If payload weight for sea-level launch is 2%, payload weight for 100k ft launch could be 4.5%.

That's a pretty significant effect.

AFAICT, the benefit is entirely reduced drag loss due to lower air density.

So why don't they build a launch site on Everest?

 

[boomtube-mk2]

None of this is going to matter if the Russians keep blowing up their satellites, thus littering LEO with enough debris you can't find a clear orbital path.

 

[Kurt Eherenman]

Straight up doesn't get you into orbit.

Orbit isn't "up" orbit is towards the horizon.

The rail gun project had a range of 100 miles compared with existing guns with a range of 30 miles. That's impressive, but it's nothing compared to what it takes to get into orbit.

FWIW, the USN pulled the plug on railgun development:

https://www.defensenews.com/naval/2...-futuristic-railgun-eyes-hypersonic-missiles/

It is quite obvious you enjoy shoving your vast knowledge and experience in people's faces with zero basis, aka, another troll. It is quite obvious you are woefully inept at understanding the latest in electo magnetic technology. I suggest opening your eyes and mind, and start reading about these efforts instead of admonishing those that have.